This invention relates to microcomputer-controlled gas burner control systems which utilize an electrical resistance igniter.
So-called hot surface ignition systems are gas burner control systems which utilize an electrical resistance igniter to ignite gas. In such systems, the igniter is electrically energized for a predetermined time period, sometimes referred to as the igniter warm-up time, to enable it to reach a temperature sufficiently high to ignite gas.
There are several manufacturers of igniters used in such systems. An igniter from any one manufacturer, because of its particular material composition, mass, and physical configuration, will generally heat up at a different rate to a different final temperature than an igniter from another manufacturer. For example, when energized at 115 volts, igniters from one manufacturer may heat up to a temperature sufficient to ignite gas, approximately 1600.degree. F., in approximately 5 seconds, and to a relatively stable final temperature of approximately 2500.degree. F. when energized for 20 seconds or longer. An igniter from another manufacturer may require more or less time to heat up to 1600.degree. F. and may attain a lower or higher final temperature. The rate of temperature change and the final temperature attained also depends on the value of the applied voltage. Specifically, when the applied voltage is less than 115 volts, the igniter heats up slower and attains a lower final temperature than when energized at 115 volts; when the applied voltage is greater than 115 volts, the igniter heats up faster and attains a higher final temperature.
Hot surface ignition systems include a control module which, among other functions, establishes the length of the igniter warm-up time period. When it is known that a particular igniter having a fast warm-up time will be used, the length of the igniter warm-up time period can be established at a relatively low value, for example, at 15 seconds. However, when the particular igniter to be used has a slow warm-up time or it is desirable that the system is to be usable with either fast or slow warm-up time igniters, the length of the igniter warm-up time period is established at a relatively large value, for example, at 45 seconds.
With regard to system operation, the 45-second igniter warm-up time period presents no particular problem. It merely establishes that upon a call for heat, 45 seconds will be provided to enable the igniter to attain gas ignition temperature. The 45-second time period is, however, a disadvantage with regard to testing the system on the assembly line of the device incorporating the system.
Specifically, in the assembly line of the device such as a furnace or boiler utilizing the system, the system is tested to determine that it operates properly. Among tests performed is a test to determine that the igniter does, in fact, ignite gas. Unless the function of the control module is bypassed or altered in some manner for this test, the igniter will be energized for the igniter warm-up time period established by the control module. Thus, when the established igniter warm-up time is 15 seconds, a test time of 15 seconds is expended; when the established warm-up time is 45 seconds, a test time of 45 seconds is expended. Since a test time of 45 seconds, and to a lesser extent, a test time of 15 seconds, are significant cost factors, particularly in a high-volume assembly line, it is desirable to reduce such test times. A reduction of such test times is feasible since the 15-second and 45-second time periods allow for the worst operating conditions that may be encountered by the igniter, such as extremely low voltage, and are considerably longer than the actual time required for the igniter to heat up to gas ignition temperature under the more favorable operating conditions existing in an assembly line test. It is also desirable to accomplish such reductions in test times without adding cost to the system.